The present invention relates to projection devices by means of which selected images may be projected onto a viewing screen. More particularly, the invention relates to such a device for selecting a transparency, out of a plurality of transparencies arranged in a predetermined sequence, for projecting the image of only the selected transparency onto a viewing screen.
In the past, many devices have been produced by means of which a selected image could be projected onto a viewing screen in order to inform the viewer that, for example, certain actions should be taken, certain machinery conditions existed, etc. Such devices, referred to as "read-outs" employed a negative or transparency having a plurality of images thereon. Such transparencies have been mounted in housings for cooperation with a plurality of projection systems. If 12 images were located on the transparency, for example, a like number of projection systems, including lamps, lens sets, etc., must also be provided within the housing. In order to project the desired image of the transparency onto the viewing screen, it was necessary to select the proper lamp and then deliver power to it for illumination. An example of such a device has been shown in U.S. Pat. No. 3,324,765.
It is quite apparent that, with these prior art devices, the number of images which can be projected onto a viewing screen from a single unit is dependant upon several factors, including the maximum allowable size of the housing containing the transparency, projection systems, etc; the quality of the optics in each projection system; the size of the image of the transparency which is to be projected; the size of the viewing screen; and the desired size and resolution quality of the image projected onto the screen. Further, as the unit is enlarged to allow the projection of additional images, its cost increases in direct proportion because each additional image requires the employment of an additional projection system.
It has also been known in the prior art to provide a single projection system, into which a plurality of transparencies may be moved, for projection of multiple images of the transparencies onto a screen. However, these devices require that the transparencies be moved into the projection system in their arranged sequence, resulting in the projection of each image seriatim. An example of such a device has been shown, for example, in the slide projector and carrier described and illustrated in U.S. Pat. No. 3,324,765.
Prior art devices of this type are satisfactory for use when it is acceptable to align a transparency with a projection system, project its image onto a screen, move the next transparency into alignment, project it onto the screen, and so forth around the carrier until the first slide is again positioned in alignment with the projection system.
However, none of these prior art devices have satisfactorily met the requirement of an inexpensive apparatus for the projection of a single image, specifically selected from a seriation of transparencies. In other words, it has become desirable and necessary to provide an apparatus having a single projection system which may be utilized in combination with a large number of transparencies, which allows projection of any selected transparency without having to work through the series of transparencies.